1. Technical Field
The present invention relates to oxidation catalyst, and particularly to diesel oxidation catalyst containing palladium as a cost effective partial or total substitution for platinum.
2. Background Art
Emission legislation has imposed increasingly stringent regulations on exhaust waste material emission controls. These waste materials include hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOx) and particulate matter (PM).
Oxidation catalysts, and diesel oxidation catalysts (DOCs) in particular, have been used in exhaust emission control system for delivering one or more of the following functions: 1) remove HC and CO from the exhaust gas as soon as possible after a cold-start; 2) maintain operation through a wide temperature range depending on the diesel application; 3) oxidize excess fuel for an active regeneration process to remove trapped PM; and 4) oxidize nitrogen monoxide (NO) to form nitrogen dioxide (NO2).
Conventional oxidation catalysts use platinum as the key precious metal-based catalytic material. However, the conventional oxidation catalysts have been met with limited use partly due to platinum's increasing unavailability and its high cost. There is a continuing need for oxidation catalysts that are more cost effective while delivering relatively comparable or better performance in reducing waste materials from the exhaust stream.